\\[-1.8ex] Soil Heterogeneity & $-$0.246 & $-$0.235 & $-$0.227 & $-$0.194 \\ 
  & (0.172) & (0.172) & (0.152) & (0.150) \\ 
\\[-1.8ex] 
Observations & 21,671 & 21,671 & 21,440 & 21,440 \\ 
R$^{2}$ & 0.607 & 0.608 & 0.620 & 0.627 \\ 
